The present invention is in the field of film thickness measurement methods and film thickness measurement devices.
This invention relates to methods of measuring film thickness. More specifically, this invention relates to a capacitive measurement method useful in determining lubricant film thickness on substrates such as magnetic disks.
Monomolecularly-thick perfluoropolyether lubricants are used for lubrication of magnetic thin-film rigid disks and metal-evaporated magnetic tapes which are crucial to the durability of the head and medium surfaces. Monomolecularly-thick lubricant films are also being developed for lubrication of microdevices, commonly referred to as microelectromechanical systems (MEMS). Uniformity of these monolayer films in the lateral dimension on the order of a few nm is critical for producing surfaces with consistent tribological performance. Present techniques to measure the thickness of such films include X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, ellipsometry, and optical surface analysis. The first three of these methods produce point measurements and require a substantial amount of time to map a surface. Optical surface analysis is best suited to obtain lubricant film thickness maps, but is limited in vertical resolution of the lubricant film thickness in comparison to the other methods. Lateral resolution of the optical analysis method also ranges from about 10 to 200 xcexcm.
It is thus an object of the present invention to develop a measurement method which can quickly, nondestructively and accurately map lubricant film thickness and characterize lubricant depletion with a lateral resolution on the nanometer scale.
Although described with respect to the field of lubricant film thickness measurements, it will be appreciated that similar advantages of quick, non-destructive capacitive measurements, as well as other advantages, may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes capacitive film thickness measurement devices and measurement systems. The invention also includes machines or instruments using those aspects of the invention. The present invention may be used to upgrade, repair, or retrofit existing machines or instruments of these types, using methods and components known in the art. The present invention also includes methods and procedures using these devices. The methods and procedures of the present invention may be applied using procedures and protocols known and used in the arts to which they pertain.
Included in the present invention is a film thickness measurement device utilizing an atomic force microscope (AFM). The AFM has a platform for supporting a film-coated conductive substrate. The AFM is configured to move a conductive probe along a path over the substrate. The conductive probe is adapted to oscillate during a first pass over a portion of the path so as to periodically contact the substrate. The AFM then lifts the probe a distance above the substrate and passes the probe for a second pass over that portion of the path.
During the second pass, the probe is at a sufficient distance from the surface of the substrate so as to not contact the film coating during the pass. A resonant capacitor sensor is also placed in connection with the conductive probe. A device is used to generate an electric field between the conductive probe and the film-coated conductive substrate. A capacitance-measuring device then measures the capacitance between the substrate and the probe while the probe is separated a distance from the substrate during a second pass over a portion of the substrate.
The AFM may also have a liquid-tight container adapted to maintain a liquid layer over the film-coated conductive substrate. The liquid layer should be of sufficient thickness to at least partially submerge the probe while the probe is separated from the film-coated substrate. It is preferred that the liquid be of a higher dielectric constant than the film.
Also included in the present invention is a method for measuring film thickness. In the method, a film-coated conductive substrate is placed upon a sample platform of an atomic force microscope (AFM). The AFM moves a conductive probe along a path over the substrate, the conductive probe adapted to oscillate during a first pass over a portion of the path so as to periodically contact the film-coated substrate. The probe is adapted to then pass along the path at a distance above the surface during a second pass over that portion, whereby the probe does not contact the surface. The conductive probe has a resonant capacitor sensor disposed thereon. An electric field is then generated between the conductive probe and the film-coated conductive substrate. The capacitance between the conductive probe and the film-coated conductive substrate is then measured over a second pass. The acquired measurements of capacitance are then used to calculate film thickness at each region of interest along the path.